Automatic transmissions have been used for a considerable time in different types of motor vehicles, such as, for example, trucks of medium and heavy weight. Varying from most passenger car transmissions, commercial vehicle transmissions exhibit not only a greater number of gear positions, but include certain gears, which are not provided for use in normal driving operations and are designed to be predominate for starting operations of a loaded vehicle, and/or for use on steep inclines and/or for maneuvering. These additional gears permit very slow movement at a very high torque which is transferred to the gears. In the following, these additional gears are designated as “creeper gears”, while the gears used generally for normal driving are termed “fast gears”.
Since automatized gear selection apparatuses show in many respects essential advantages in comparison to a manual gear choice made by the driver, these apparatuses are increasingly being installed for heavy vehicles, which employ creeper gears. When this is the case, then, within arm's reach of the driver, at least one gear selection succession is presented, which exhibits three adjustments, namely D, N and R. In the automatized gear range shifter apparatus, in the D-position of the range of gear positions, automatically the respective optimal forward gear is selected without the involvement of the driver or following a displayed confirmation, the driver makes an optional setting of the D-position. When this occurs, the gear to be engaged, for example, is determined with consideration given to: speed of rotation of the motor, motor load, vehicle speed, acceleration, charted motor performance, and possibly additional parameters. In the N-position of the gear range shifter, the transmission is shifted into a neutral position and in the R-position, the reverse gear is engaged, that is to say, the most applicable of various reverse gears is selected.
From his own selection, the driver additionally has a functionally extended gear range shifter by which he can influence an automatic shifting apparatus. This can include, for example, additional shifting positions available to the gear range shifter positions, which can be designated as first, second, third and the like. However, these additional positions considerably diminish the number of the shiftable forward gears. Alternative to this or in addition thereto, the driver often cannot activate, in the given range of gears integrated in the gear range shifter, either an up or down shift. In this situation, the transmission is initiated, to shift one stage up or down from an automatically selected gear. On the other hand, the driver may choose a fully manual mode, for example, by an additional engagement at the M-position of the gear range shifter and shifts the transmission in a method similar to a Tiptronic-Shift wherein the choice is made in a sequential manner and each shifting activation corresponds to a gear change in a chosen direction.
An automatic shifting apparatus in any case cannot reliably discern whether a driver, by his setting of the gear range shifter into the D position of the forward gear range or into the R-position of the reverse gear range, has the intention of moving the vehicle with millimeter precision at creep speed, in order, for example, to carry out an intricate vehicle maneuver or whether the driver plans a normal startup or reverse action. On this account, for the choice of the creep speed mode or the fast mode, it is necessary that an intention of the driver be separately determined and announced.
DE 40 06 653 A1 makes known a shifting apparatus for the semi-automatic shifting of multistage gear change transmissions, which has a gear choice apparatus and a gear range shifter. The said gear range shifter is designed as a rotational shifting means and, besides governing the positions D, N and R, the device can additionally control an M-position, which enables a manual selection of gears. Additionally it is possible that still further positions for shifting programs (not further detailed), namely X1 and X2 can be provided, whereby following the direction of the said rotational shifting means the shift series succession M-D-N-R-X1-X2 becomes available.
Even if, in an extension of the disclosure of DE 40 06 653 A1, an assumption might be made, that the driving programs X1 and X2 are provided for creeper gears in a forward or in a reverse direction, then, in spite of the operational security of the gear range shifter, which passes through a great number of shifting positions, this security is strongly limited, especially in a situation of operation without foresight—that is to say, operation without the driver giving attention to the involved operating elements. In addition, a gear range shifter must be activated to allow exiting from the driving programs X1 or X2 and to obtain the choice of the normal driving position, the same must skip over a great many interposed gear stages.
If, for example, an assumption is made, that X1 represents a creeper gear program for forward movement, a driver finds himself under an obligation to drive a few meters in the direction of a loading ramp or some other targeted position. If, at the desired position and then he would want to precisely position the vehicle, he is obliged to first choose the D-position, in order to subsequently shift through the N-position and the R-position into the X1-position. A smooth switchover between creeper gear and fast gear, in this case, is not possible. In addition, the risk exists of an unforeseen choice of a wrong gear range and especially a gear range in a direction contrary to that desired.
DE 100 16 582 A1 and DE 101 05 749 A1 disclose similar gear range shifters, wherein the positions for forward and reverse creeping gear, however, are to be found at end locations of the rotational scale on different sides and thereby the shift-positions between the reverse travel gear range and the reverse creep gear range are proximal to one another and thus permit safe gear changing. In any case, the switchover between the creep travel gear range for forward and reverse gearing in this instance, requires a shifting movement passing over a number of other gear range. This is quite unfavorable for a maneuvering operation, which often is marked by repeated and quick gear changing between forward and reverse creeper gears.
Giving consideration to the above background, the purpose of the invention is to present a control procedure for an automatic transmission, wherein, by means of a gear range shifter, in a simple and intuitive operational manner for the driver, a change of a gear range can be employed both between the forward gear range and the reverse gear range, as well as between a fast gear mode and a creeper gear mode.
This purpose is achieved by the features of the principal claim, while advantageous embodiments and developments of the invention can be inferred from the subordinate claims.